308 Barrel with 1:12 twist, what to use?

[Bawlmore]

Just like the title states, I have a 25" barrel chambered in 308 Winchester, with a 1:12 twist and 4R rifling... just wondering what's the best bullet weight to use here. I know it'll stabilize 155gn but will 175gn work here too? I'm new to twist rates so any advice would be greatly appreciated.

 

[Down South]

I know guys that run 185 juggernauts in 12 twist barrels with good success but that's in 30-32 inch barrels running them hard.

 

[oldhoward]

I have a Remington with a 1:12 twist 26 inch barrel. Best accuracy has been with 155gn bullets. Anything above 168 gn bullets open up the groups. I have not found any bullets in the 175 and up range that shoot well in my rifle. Each rifle is different so your rifle may shoot them better than mine.

 

[Bawlmore]

I have a Remington with a 1:12 twist 26 inch barrel. Best accuracy has been with 155gn bullets. Anything above 168 gn bullets open up the groups. I have not found any bullets in the 175 and up range that shoot well in my rifle. Each rifle is different so your rifle may shoot them better than mine.

How far out have you been pushing the 155s? I doubt I'll ever need to take them past 1,050 yards.

 

[watercam]

You would be hard pressed to keep 155s supersonic out to 1K with a 25" barrel. Palma competitors use 30-32" barrels to keep velocity at the muzzle at 2950 and above and remain somewhere in 1200+ fps range on target. 175s will make it and the 185s/190s will do even better. I had good luck with H4350 pushing 185s to around 2750 at the muzzle and 1300+ at the target with a 30" so you can expect about 125 fps less than that with a 25. There are heavier bullets that the F-TR folks seem to like but too much recoil for me in a coat and sling.

 

[oldhoward]

How far out have you been pushing the 155s? I doubt I'll ever need to take them past 1,050 yards.

Hi, I have shot to 800 yards with the 155's. I currently don't have a place to shoot further. Shooting off of a rickety table rest groups about 5.5 inches on a good day and a lot bigger on a bad day, it is always windy where I shoot.

 

[Bawlmore]

Hi, I have shot to 800 yards with the 155's. I currently don't have a place to shoot further. Shooting off of a rickety table rest groups about 5.5 inches on a good day and a lot bigger on a bad day, it is always windy where I shoot.

5.5inches at 800 yards is about the best I can shoot anyway, so I don't think I'll have any complaints!

 

[alf]

Just like the title states, I have a 25" barrel chambered in 308 Winchester, with a 1:12 twist and 4R rifling... just wondering what's the best bullet weight to use here. I know it'll stabilize 155gn but will 175gn work here too?

I had a 700 Varmint with a 12 twist, & it shot 190 SMK's just fine.

 

[oldhoward]

I had a 700 Varmint with a 12 twist, & it shot 190 SMK's just fine.

Hi Alf would you mind sharing your load data? I also have a varmint and so far it don't like heavy bullets above 168 gn.

 

[alf]

Hi Alf would you mind sharing your load data? I also have a varmint and so far it don't like heavy bullets above 168 gn.

I was afraid someone would want my load.....

I don't have my notes anymore for that gun...sorry.

 

[BoilerUP]

My 700 ADL Varmint with 26" 1:12 barrel likes the 168gr Amax.

A 168gr TAP clone load (44.4gr Varget in Hornady brass with WLR @ 2.81" COAL) gives me 2713fps, while 42.4gr 8208XBR in Win brass with WLR @ 2.81" gives me 2677fps - velocities per Magnetospeed V2.

 

[Laurie]

Give the Berger 185gn BT Juggernaut a try. When it was first around, its designer Bryan Litz was winning long-range sling matches with it in a 30-inch 1 in 13-inch twist barrel, although he noted the twist was too slow, and rebarrelled to a 12-inch twist the following year.

At that time, seven maybe eight years ago, an Sg factor (coefficient of stability) factor of 1.40 was recommended as calculated by the Miller Rules formula. (Theoretically anything above 1.000 is stabilized, but considerably higher values are actually needed.) This is a quick and not too dirty calculator available as an Excel spreadsheet to download if you Google it. You do need the bullet length though - it, the calibre, and the twist rate are the major factors in determining the likely Sg value. (For Berger bullets, go on the company website, click on Ballistics then take the bottom option Twist Rate Calculator. All Berger match bullets are available in its menu and it's very easy to use.)

Weight affects the results too, likewise speed, but less than you think and in fact for any given calibre / bullet length / MV combination the heavier the bullet the higher the Sg and the 'slower; the twist needed. People traditionally talked bullet weights re required twists because as they become heavier in a calibre, they become longer - usually. Nowadays, we have so many very long for weight and calibre bullets around thanks to long-nose designs to reduce drag and increase BC values, weight alone becomes even less reliable as an indicator.

Taking 30 cal and three pairs of bullets in your 12 inch twist barrel:

168gn Sierra MK (1.215" OAL) .......................... 1.72 Sg
168gn Berger Target Hybrid ((1.296" OAL) ......... 1.43 Sg
(assuming 2,700 fps MV)

175gn Sierra MK (1.240" OAL) ................................. 1.67 Sg
175gn Berger Target BT Long Range (1.279" OAL) .... 1.52 Sg
(assuming 2,600 fps MV)


190gn Sierra MK (1.353) .................................. 1.39 Sg
185gn Berger Juggernaut (1.353) ...................... 1.35 Sg
(assuming 2,500 fps MV)

These are all in standard ballistic conditions (59-deg F; 29.92 inches mercury atmospheric pressure). If you shoot in the Arctic in winter on the foreshore, the Sg values are depressed and you may need a 'faster' twist. If you shoot at 7,000 ft ASL (as in Raton NM) in 80 or 90 deg F, the SG values rise considerably and you can 'get away' with a markedly 'slower' twist.

Noe there is another twist (pun!) to the tale. After years and years of ballisticians recommending 1.4 Sg or higher as a target, a couple of years ago, it was raised to 1.5 by Bryan Litz / Berger Bullets. This was because recent research showed that whilst bullets given Sg values above ~1.3 shoot and group fine and appear fully stabilised, they create some extra drag (same effect as reducing the BC) up to 1.5 where everything is now peachy.

So, if you take the 168gn Berger Hybrid in your 12 inch barrel which in give or take conditions is on or just above the old recommended 1.4, go on the Berger twist calculator and it'll tell you it is 'marginally stabilised', and quote the BC loss - 3% is the calculation. So, a bullet with a nominal average G7 BC of 0.269 reduces to an estimated 0.258, still higher than the shorter, blunter Sierra MK's calculated 0.243.

The Juggernaut at 1.35 loses a little more Berger saying it's minus 4% or its nominal G7 value dropping from 0.283 to ~0.272, still a very high BC compared to equivalent competitors.

So, all of the above (and many more) can be used in your barrel, but some will lose a bit of efficiency. Avoid most VLDs and Berger Hybrids weighing more than 168, maybe 175gn as their additional length really drops Sg values and serious stability problems arise. For a cheap, well made and short to mid range bullet, the Sierra 168 and 175 (plus the similar Nosler CC models) will shoot very well in your barrel. For a step up at a bit of hit in your wallet, the 175gn Berger BT Target Long-Range (not same weight Berger VLD) is an easy to tune very well mannered bullet that has a high BC and is fully stabilised in a 12 twist barrel. Also, try the 185gn Juggernaut and see how it works - an excellent bullet for 26-inch barrel rifles for long ranges. It should be OK in summer weather and you'd be able to live with a slight drop in its BC.

 

[Bawlmore]

Give the Berger 185gn BT Juggernaut a try. When it was first around, its designer Bryan Litz was winning long-range sling matches with it in a 30-inch 1 in 13-inch twist barrel, although he noted the twist was too slow, and rebarrelled to a 12-inch twist the following year.

At that time, seven maybe eight years ago, an Sg factor (coefficient of stability) factor of 1.40 was recommended as calculated by the Miller Rules formula. (Theoretically anything above 1.000 is stabilized, but considerably higher values are actually needed.) This is a quick and not too dirty calculator available as an Excel spreadsheet to download if you Google it. You do need the bullet length though - it, the calibre, and the twist rate are the major factors in determining the likely Sg value. (For Berger bullets, go on the company website, click on Ballistics then take the bottom option Twist Rate Calculator. All Berger match bullets are available in its menu and it's very easy to use.)

Weight affects the results too, likewise speed, but less than you think and in fact for any given calibre / bullet length / MV combination the heavier the bullet the higher the Sg and the 'slower; the twist needed. People traditionally talked bullet weights re required twists because as they become heavier in a calibre, they become longer - usually. Nowadays, we have so many very long for weight and calibre bullets around thanks to long-nose designs to reduce drag and increase BC values, weight alone becomes even less reliable as an indicator.

Taking 30 cal and three pairs of bullets in your 12 inch twist barrel:

168gn Sierra MK (1.215" OAL) .......................... 1.72 Sg
168gn Berger Target Hybrid ((1.296" OAL) ......... 1.43 Sg
(assuming 2,700 fps MV)

175gn Sierra MK (1.240" OAL) ................................. 1.67 Sg
175gn Berger Target BT Long Range (1.279" OAL) .... 1.52 Sg
(assuming 2,600 fps MV)


190gn Sierra MK (1.353) .................................. 1.39 Sg
185gn Berger Juggernaut (1.353) ...................... 1.35 Sg
(assuming 2,500 fps MV)

These are all in standard ballistic conditions (59-deg F; 29.92 inches mercury atmospheric pressure). If you shoot in the Arctic in winter on the foreshore, the Sg values are depressed and you may need a 'faster' twist. If you shoot at 7,000 ft ASL (as in Raton NM) in 80 or 90 deg F, the SG values rise considerably and you can 'get away' with a markedly 'slower' twist.

Noe there is another twist (pun!) to the tale. After years and years of ballisticians recommending 1.4 Sg or higher as a target, a couple of years ago, it was raised to 1.5 by Bryan Litz / Berger Bullets. This was because recent research showed that whilst bullets given Sg values above ~1.3 shoot and group fine and appear fully stabilised, they create some extra drag (same effect as reducing the BC) up to 1.5 where everything is now peachy.

So, if you take the 168gn Berger Hybrid in your 12 inch barrel which in give or take conditions is on or just above the old recommended 1.4, go on the Berger twist calculator and it'll tell you it is 'marginally stabilised', and quote the BC loss - 3% is the calculation. So, a bullet with a nominal average G7 BC of 0.269 reduces to an estimated 0.258, still higher than the shorter, blunter Sierra MK's calculated 0.243.

The Juggernaut at 1.35 loses a little more Berger saying it's minus 4% or its nominal G7 value dropping from 0.283 to ~0.272, still a very high BC compared to equivalent competitors.

So, all of the above (and many more) can be used in your barrel, but some will lose a bit of efficiency. Avoid most VLDs and Berger Hybrids weighing more than 168, maybe 175gn as their additional length really drops Sg values and serious stability problems arise. For a cheap, well made and short to mid range bullet, the Sierra 168 and 175 (plus the similar Nosler CC models) will shoot very well in your barrel. For a step up at a bit of hit in your wallet, the 175gn Berger BT Target Long-Range (not same weight Berger VLD) is an easy to tune very well mannered bullet that has a high BC and is fully stabilised in a 12 twist barrel. Also, try the 185gn Juggernaut and see how it works - an excellent bullet for 26-inch barrel rifles for long ranges. It should be OK in summer weather and you'd be able to live with a slight drop in its BC.

I'm going to read through this once or twice when I have an hour to kill, thank you for the literal essay of information!

 

[BOB LEE SWAGGER]

I have an AI .308 1:12 twist on order. Consistently helpful advice from Laurie!

 

[boltgunluvr]

my 1 in 12 has no issues up and including to the 190gr.

 

[4xforfun]

My 1-12 LOVES the 200 Hybrid. But...@ 2900 out of a WSM.,,,about 300 FPS faster than your 308 can handle.

 

[jlow]

Just like the title states, I have a 25" barrel chambered in 308 Winchester, with a 1:12 twist and 4R rifling... just wondering what's the best bullet weight to use here. I know it'll stabilize 155gn but will 175gn work here too? I'm new to twist rates so any advice would be greatly appreciated.

I have an Accuracy International AT with factory 1:12 twist 24” barrel and it loves the 185 Juggs. Absolutely no problem with the 175gr of course as that would normally be the workhorse bullet for this gun.

 

[Bawlmore]

My 1-12 LOVES the 200 Hybrid. But...@ 2900 out of a WSM.,,,about 300 FPS faster than your 308 can handle.

Barrel isn't attached to an action at the moment, and I need to chop off the tenon and rethread... so I'll have to ream a new chamber, 300WSM is an option.

 

[Laurie]

Different case-head / bolt face diameters between the pair (308 Win / WSM), so simple rebarrelling isn't an option.

I'm afraid Berger's analysis of the 200gn Hybrid in a 12-inch twist rate barrel isn't exactly promising. 300 extra fps frankly barely improves the Sg value (1.10 to 1.14 when you're looking for values around 1.4, better still 1.5).

The minimum recommended twist rate is 10.3 for this bullet at 2,900 fps MV.

Here's the Berger summary result:

Stability Analysis


Your bullet is MARGINALLY STABLE.
Your bullet stability is marginal. You may shoot good groups under these conditions, but the BC of the bullet will not be optimized.


SG = 1.14
Bullet BC (G7):0.320
Adjusted BC for 1 in 12" Twist: 0.285
Your BC is being compromised by:11%
Minimum Twist Recommended:1 in 10.3"


Ignoring the loss of BC that drops the 200gn Hybrid's superb characteristics in fully stabilised form to around that of the 185gn Juggernaut, such a combination that produces Sg values in the 1.1s is likely to be seriously inconsistent depending on the external environment. It may work at higher altitudes in good summer weather, but fail to to even stabilise bullets and produce groups on another location and in a colder season.

(Incidentally, use of the 200gn Hybrid as opposed to most of the other bullets you're considering isn't just a rifling twist issue. The heavier Hybrids are VERY long bullets and need to have chambers with long freebores to allow the bullet to be seated correctly. For this bullet, COAL will be around the 3-inch mark with the ogive just off the start of the rifling lands.)

 

[4xforfun]

Different case-head / bolt face diameters between the pair (308 Win / WSM), so simple rebarrelling isn't an option.

I'm afraid Berger's analysis of the 200gn Hybrid in a 12-inch twist rate barrel isn't exactly promising. 300 extra fps frankly barely improves the Sg value (1.10 to 1.14 when you're looking for values around 1.4, better still 1.5).

The minimum recommended twist rate is 10.3 for this bullet at 2,900 fps MV.

Here's the Berger summary result:

Stability Analysis


Your bullet is MARGINALLY STABLE.
Your bullet stability is marginal. You may shoot good groups under these conditions, but the BC of the bullet will not be optimized.


SG = 1.14
Bullet BC (G7):0.320
Adjusted BC for 1 in 12" Twist: 0.285
Your BC is being compromised by:11%
Minimum Twist Recommended:1 in 10.3"


Ignoring the loss of BC that drops the 200gn Hybrid's superb characteristics in fully stabilised form to around that of the 185gn Juggernaut, such a combination that produces Sg values in the 1.1s is likely to be seriously inconsistent depending on the external environment. It may work at higher altitudes in good summer weather, but fail to to even stabilise bullets and produce groups on another location and in a colder season.

(Incidentally, use of the 200gn Hybrid as opposed to most of the other bullets you're considering isn't just a rifling twist issue. The heavier Hybrids are VERY long bullets and need to have chambers with long freebores to allow the bullet to be seated correctly. For this bullet, COAL will be around the 3-inch mark with the ogive just off the start of the rifling lands.)

All could be true..and I can't argue your facts. It is just those damm 5 inch 10 shot groups at 1k that are doing all of the arguing!!